Galileo Galilei was born in Pisa, Italy in 1564. His father wanted him to
be a doctor. Galileo wanted to work with mathematics. He took a job teaching
math to university students. Galileo was also interested in astronomy. He
built a
telescope to help him study the sky. Galileo first discovered that the
Moon had
mountains just like Earth. He also discovered 4 of Jupiter's moons. Using
his telescope, Galileo made many observations of our Solar System. He came
to believe that the idea that the Sun and other planets orbited around the
Earth was not correct. Galileo felt that an
astronomer named Copernicus
had a better idea. Copernicus believed the Earth and other planets moved
around the Sun.

During Galileo's time, the Catholic Church was very powerful and it taught
that the Earth was the center of the universe.
Galileo was told not to write
or say that the Earth orbited the Sun. He could not be silent. In 1632,
Galileo published a book that said the Earth orbited the Sun. The Catholic
Church arrested him and put him on trial. He was still under arrest at the time of his death on January 8, 1642.